Invincible in battle

The new species has fewer lower vertebrae and more robust and flattened ribs than its relative.

Bill Stanley, from the Field Museum of Natural History, Chicago, US, said: "The expanded backbone and the strength of this animal has fascinated biologists for over 100 years. Until now there has been only one species known with this bizarre vertebral column.

"We hypothesise that this shrew - with its expanded backbone and associated musculature - can crawl in-between the trunk and leaf bases of trees to allow access to concentrated food resources that would normally be protected from predation.

"The same mechanism could be used for getting under logs or rocks which they could lift out of the way."

Image caption
The shrews have interlocking vertebrae which form an expanded backbone

The unique Hero Shrew has twice the number of lower vertebrae humans do and a spine four times more robust relative to its body size.

This is just one example of a new mammal but there's still a lot more to this planet we have to learn aboutBill Stanley, The Field Museum, US

Its strength has received legendary status in the African Congo, where parts of the animal are worn as a talisman in battle. The wearers believe it could make them invincible to spears or bullets.

As no other forms of its expanded back bone have previously been discovered, many zoologists believed the Hero Shrew was an example of punctuated equilibrium - which is where dramatic evolutionary changes take place very quickly.

Missing link

But Mr Stanley explained that there are aspects of S. thori's vertebral column that "suggest it's a transition between the regular shrew and the original species of Hero Shrew", which could shed light on how quickly it evolved.

He told BBC News it had the potential to be a "missing link" to how the Hero relates to other shrews.

"The age of discovery is not over. People think we have everything sussed out but the collections contained within institutions [such as the Field Museum] allow us to figure out what makes this planet tick.

"This is just one example of a new mammal but there's still a lot more to this planet we have to learn about."

Kristofer Helgen, of the Smithsonian Institution's National Museum of Natural History, who was not involved with the study, said it was an "outstanding find".

"The anatomy of this new species gives important clues about the evolution of the unusually strong spine in this group of shrews, and the authors of the paper provide the first compelling explanation for the adaptive significance of the unusual spine."